A number of needleless syringes are disclosed, for example, in International Patent Applications WO 94/24263 and WO 96/25190. These syringes are commonly used for delivery of therapeutic compounds and compositions to skin, muscle, blood or lymph. The syringe can also be used in conjunction with surgery to deliver therapeutics to organ surfaces, solid tumors and/or to surgical cavities (e.g., tumor beds or cavities after tumor resection), as well as for prophylactic, diagnostic or other medical treatments. These syringes generally have an upstream portion, which contains, or is arranged to be connected to, a source of fluid under pressure, a downstream nozzle portion, and, between the upstream and downstream portions, an intermediate portion which accommodates a dose of a therapeutic agent to be delivered, and an actuator mechanism for initiating a flow of the fluid from the source so that the dose is entrained in the fluid flow through the intermediate portion and hence to and through the nozzle for delivery to a target site.
In these syringes, the therapeutic agent is provided in a sealed capsule having upstream and downstream rupturable diaphragms. The diaphragms are sealed together about their edges and contain in the chamber formed therebetween a dose of the agent which is to be delivered. Upon release of a compressed gas, the gas pressure quickly builds up behind the capsule until the differential pressure across the capsule becomes sufficient to burst the capsule diaphragms, thus releasing through the spent capsule and nozzle a gas flow in which the therapeutic agent is entrained.
Although this arrangement has proved to be very successful, it would be desirable to provide a capsule which is cheap to manufacture, from which the full dose of drug will reliably be flushed out and entrained in the gas stream, and which is sufficiently robust to avoid the production of debris.